A gene that regulates bone growth and muscle metabolism in mammals may also help promote brain maturation, cognition and learning in humans, a new study has found. The research by Harvard Medical School in the US provides a dramatic illustration of evolutionary economising and creative gene retooling mechanisms that contribute to the vast variability across species that share nearly identical set of genes yet differ profoundly in their physiology. The research shows that osteocrin – a gene found in the skeletal muscles of all mammals and well-known for its role in bone growth and muscle function – is completely turned off in rodent brains yet highly active in the brains of non-human primates and humans.

Osteocrin was found predominantly in cells of the neocortex, the most evolved part of the primate brain, which regulates sensory perception, spatial reasoning and higher-level thinking and language in humans. The gene’s marked presence in an area of the brain responsible for higher-level function and thought, suggesting a possible role in the development of cognition, a cardinal feature that distinguishes the brains of human and nonhuman primates from those of other mammals, researchers said. Brain development in primates is profoundly affected by sensory experience and social interactions.

Scientists have long sought to unravel genes in the brain that are turned on and off by experiences to fuel the rise of brain functions unique to such complex species. The finding shows that osteocrin is precisely one such gene, activated by sensory stimulation. This is the first illustration of evolutionary gene repurposing in the brain. “We have uncovered what we believe is a critical clue into the evolution of the human brain, one that gives us a glimpse into the genetic mechanisms that may account for differences in cognition between mice and humans,” said Michael Greenberg, from Harvard Medical School.

For their experiments, the team analysed RNA levels, the molecular footprints of gene activity in the brain cells of mice, rats and humans. Although many of the same genes were activated in both mouse and human brain cells, a small subset of genes was activated solely in human brain cells, researchers said. The bone gene osteocrin was most highly expressed in the human brain, yet completely shut off in the brain cells of mice. The study appears in the journal Nature.